Question

An electron and a proton enter a magnetic field perpendicularly. Both have same kinetic energy. Which of the following is true

• A. Trajectory of electron is less curved
• B. Trajectory of proton is less curved
• C. Both trajectories are equally curved
• D. Both move on straight line path

Answer 1

Answer: (B)

Trajectory of proton is less curved

Answer 2

By using $r = \frac { \sqrt { 2 m k } } { q B }$ ; For both particles $q \rightarrow$ same,

$B \rightarrow$same, $k \rightarrow$ same

Hence $r \propto \sqrt { m }$ $\Rightarrow$ $\frac { r _ { e } } { r _ { p } } = \sqrt { \frac { m _ { e } } { m _ { p } } }$

$m _ { p } > m _ { e }$ so $r _ { p } > r _ { e }$

Since radius of the path of proton is more, hence it's trajectory is less curved.